The present invention relates to carbon dioxide capture systems, and more specifically to carbon dioxide capture systems that prevent carbon dioxide present in flue gases from industrial facilities, such as power plants and steel mills, from being exhausted into the atmosphere.
Due to recent global warming, the polar icecaps have been melting, causing a rise in the sea level. Recent changes in climate have caused unusual weather phenomena around the world. Global warming is known to be attributed to increased greenhouse gas emissions. International agreements have been signed to restrict the emission of carbon dioxide. Attempts to suppress the emission of carbon dioxide by the introduction of carbon credits become economic issues in individual countries around the world. Efforts to reduce the emission of carbon dioxide have been directed towards the development of alternative energy sources (such as solar energy and wind energy) capable of replacing fossil fuels, and techniques for the capture and storage of carbon dioxide from fossil fuels while preventing the carbon dioxide from being released into the atmosphere. The latter techniques are called carbon capture and storage (CCS) techniques and are broadly divided into techniques for capturing carbon dioxide from power plants and steel mills and techniques for storing captured carbon dioxide in the soil or ocean.
The carbon dioxide capture techniques can be divided into post-combustion capture, pre-combustion capture, and oxy-fuel capture according to stages at which carbon dioxide is captured. The carbon dioxide capture techniques can also be divided into membrane separation, liquid phase separation, and solid phase separation techniques according to the principles of carbon dioxide capture. The membrane separation techniques use separation membranes to concentrate carbon dioxide, the liquid phase separation techniques use liquid adsorbents such as amines or aqueous ammonia, and the solid phase separation techniques use solid phase adsorbents such as alkali or alkaline earth metals.
The solid phase separation techniques are largely directed towards the development of solid phase adsorbents Carbon dioxide capture efficiency is greatly affected by the design of adsorption processes as well as the performance of solid phase adsorbents. Solid phase adsorbents can be broadly classified into organic, inorganic, carbon-based, and organic-inorganic hybrid adsorbents by the kind of their constituent materials. Solid phase adsorbents can also be classified into physical adsorbents and chemical adsorbents depending on their forms adsorbed by carbon dioxide. Representative examples of such solid phase adsorbents include: amine polymer adsorbents as organic adsorbents; zeolite-based adsorbents, alkali adsorbents, and alkaline earth metal adsorbents as inorganic adsorbents; activated carbon adsorbents modified with alkali metals as carbon-based adsorbents; and MOF adsorbents and porous silica adsorbents grafted with organic materials having an amine group as organic-inorganic hybrid adsorbents. Carbon dioxide is physically adsorbed to zeolite-based and carbon-based adsorbents. Carbon dioxide is adsorbed to the other adsorbents through chemical reactions (Energy Environ. Sci. 2011, 4, 42. ChemSusChem 2009, 2, 796).
Solid phase separation includes the steps of adsorbing carbon dioxide to a target object, and desorbing and separating the adsorbed carbon dioxide from the target object. The adsorption and desorption of carbon dioxide may occur reversibly and may be induced through heat exchange or a change in external pressure. Such carbon dioxide capture processes using dry adsorbents are classified into pressure swing adsorption (PSA) processes and temperature swing adsorption (TSA) processes by the factors they use. The PSA processes use a pressure difference and the TSA processes use a temperature difference to desorb adsorbed carbon dioxide. Generally, pressure swing adsorption processes using fixed bed adsorption columns are advantageous in capturing carbon dioxide on a small scale, and an easy-to-scale-up temperature swing adsorption processes using fluidized bed adsorption and desorption columns are advantageous in capturing a large amount of carbon dioxide from power plants or large combustion furnaces.
The present invention is intended to capture a large amount of carbon dioxide in a continuous manner using solid adsorbents and is based on a temperature swing adsorption process using fluidized bed adsorption columns and fluidized bed desorption columns. The adsorption columns and desorption columns can be divided into bubbling fluidized bed columns and diluted fluidized bed columns according to the concentration of adsorbents in operating regions. Adsorbents are present at high concentrations in the bubbling fluidized bed columns and at low concentrations in the diluted fluidized bed columns. The application of such bubbling fluidized beds and diluted fluidized beds to adsorption columns and desorption columns provides four possible combinations: i) diluted fluidized bed columns-diluted fluidized bed columns, ii) diluted fluidized bed columns-bubbling fluidized bed columns, iii) bubbling fluidized bed columns-diluted fluidized bed columns, and iv) bubbling fluidized bed columns-bubbling fluidized bed columns (“Fluidization Engineering”, D. Kunii and O. Levenspiel, Robert E. Krieger, 1977).
Korean Patent Publication Nos. 2005-0003767, 2010-0099929, and 2011-0054948 disclose fluidized bed processes for carbon dioxide capture that use dry solid adsorbents based on the concept of temperature swing adsorption using diluted fluidized bed adsorption columns and bubbling fluidized bed desorption columns. According to such solid phase separation processes based on the concept of temperature swing adsorption, however, a vast amount of energy of at least 2 GJ/t-CO2 is consumed to desorb carbon dioxide from adsorbents. This energy consumption is a cause of increased capture cost, together with the cost of the adsorbents. Thus, it is very important to develop a technology by which carbon dioxide can be effectively desorbed from adsorbents with less energy, achieving reduced capture cost.